You’ve pretty well described it. Crowded and noisy.
The center of all things is the Dealers’ Room, with tables and booths, where you can buy (and sell, a little) all sorts of stuff. From this week’s comics to 1940’s comics. Toys and games and apparel. Animation cels.
There’s an artists’ alley, where you can stand in line to get autographs, or to commission art. Many artists will do a quickie sketch for free. Others ask some money.
There’ll be autograph tables for authors, too, doing book signings, and for celebs, signing promotional photographs. Figure on some VERY long lines.
There will be big-room presentations, where 5,000 people sit in theater-style seating to listen to some bigwig talk about his studio’s upcoming movie. These are often sweetened with a celeb or two, making such presentations VERY hard to get into. The lines can run the length of the convention center.
There’ll be lesser presentations, and workshops, and demos. The coloring demo; the lettering demo; the “how to draw a horse right, damn it” demo (a classic!)
There will very likely be a masquerade, where people come out on stage in MAGNIFICENT costumes (okay, yeah, and a few beginners doing the best they can.) These usually involve a brief skit or routine. The big-group presentations can be glorious.
And a big part of the convention scene is outside the convention itself: room parties in the nearby hotels, dinner groups, clubbing, touring the city, etc. There is usually a collection of grumblers at the hotel bar: some notable SF authors go there and stay there the whole convention through.
If you’e got connections, it can be a hell of a lot of fun. If you’re by yourself, and don’t have “ins” it can be kinda lonely and boring.
After three days of this, your feet are gonna hurt.
It’s worth it!